1. Field of the Invention
A certain aspect of the present invention relates to an image processing device, an image processing method, an image forming apparatus, and a storage medium storing program code for causing a computer to function as the image processing device.
2. Description of the Related Art
With a typical image processing device for converting a color image including character images into a monochrome image, characters drawn in colors other than black (hereafter called color characters) in an original color image are converted into pale gray characters that are less noticeable than black characters. With such an image processing device, characters emphasized by the creator of a color image may become less noticeable than other normal characters. For example, in a color image, normal characters are drawn in black and characters to be emphasized are drawn in colors such as red and blue to attract the attention of readers. If such a color image is converted into a monochrome image as described above, the color characters are converted into pale gray characters that are less noticeable than black characters.
Patent document 1 discloses an image processing device that changes character properties of color characters so that the color characters are, for example, underlined or italicized when they are converted into monochrome characters. The disclosed image processing device makes it possible to convert color characters into underlined, italicized, or boldfaced black characters and thereby to make them more noticeable than normal black characters even after the conversion.    [Patent document 1] Japanese Patent Application Publication No. 8-328788
Meanwhile, in some documents, character properties such as character decorations (e.g., underline), typefaces (e.g., italic and fonts), character sizes, and character thickness have special meanings. For example, in administrative documents and scientific papers, underlines attached to characters may indicate that the characters are modified and italic alphabetical characters may be used to represent scientific names in biological classification. If such documents are converted into monochrome images with an image processing device as disclosed in patent document 1, characters that have not been modified may be underlined and words other than scientific names may be italicized. This may result in giving wrong information to readers of the documents.